lc 32 ga5e

Transcript

lc 32 ga5e

Portonovo (An), June 22-23, 2016
Recent advances of liquid crystal applications:
from novel electro-optic devices to systems
Antonio d’Alessandro
Dept. of Information, Electronic and Telecommunications
Engineering, Sapienza Univ. of Rome,
[email protected]
Department of Information Engineering, Electronics and Telecommunications
Applications of LC (from ILCC web page)
Flat panel displays
LC Optics and Applied Systems
LC Lasers and Nonlinear Optical Devices
Sensing Devices and Systems
Actuators and Haptic Devices
LC Smart Systems (Privacy Windows, Energy Saving
Films, Writing Tablets, Security Applications)
Energy Conversion
Others
A. d’Alessandro,SICL Portonovo (An) 20-23 giugno 2016
Topics of this talk
…….but which breakthrough/disruptive applications based on
LC?
Outline
Flat panel displays
A quick review of recent LCD technology
Flexible displays
Quantum dots LC displays
LCD vs OLED displays
Photonics devices
Tunable lasers
Random lasers
LC waveguides
Organic electronics (OFET, photovoltaics)
Concluding remarks
Standard TN displays
Standard TN displays
Active matrix TFT-LC displays
Light transmission through of LCD
In the Mauguin limit: d·Δn>>Φλ/π
(Δn birefringence of the liquid crystal, d thickness of the liquid crystal layer, Φ twist
angle of the liquid crystal layer, λ wavelength of the light)
Case of parallel polarizers Maugin
condition for u>> 1,
Case of TN for Φ= π/2
Switching time
Due to the faster switching time and less viewing angle dependency, the first
minimum is preferred. Cell gaps in commercially available displays are typically
around 4 μm, needing liquid crystal mixtures with Δn (birefringence) between
0.090 and 0.1050.
η
η
τr =
τf =
2
2
2
Kq
ε
⋅
Δ
ε
⋅V
−
Kq
(0
)
a
K = K11 + ( K 33 − 2K 22 ) / 4 q = π / d
Threshold voltage
NLC mixtures for low voltage displays
Voltage holding ratio and dielectric anisotropy
In plane switching (IPS) for monitor and TV LCD
IPS LCD have improved viewing angle performance.
τr =
η
η
τ
=
f
Kq 2
(ε 0 ⋅ Δε ⋅Va2 − Kq2 )
K = K11 + ( K 33 − 2K 22 ) / 4 q = π / d
High polarity LC can be used because VHR does not degrades as in TN cells.
High polarity LC have lower rotational viscosity which compensates for dependance
of switching times on K22.
In plane switching (IPS) for monitor and TV LCD
IPS LCD have improved viewing angle performance.
Vertically aligned LCD (VA-LCD)
VA-LCD operate in normally black mode
with deep dark state between crossed
polarizers -> high contrast
They require negative dielectric anisotropy
LC.
They need preferential switching direction to
avoid orientation defects.
Vertically aligned LCD (VA-LCD)
Multi domain vertically aligned (MVA) LC are used, in which substrates have
protrusions to improve viewing angle.
Patterned vertically aligned (PVA) LCD are also used with shifted electrodes.
VA-LCD and IPS LCD Advantages
IPS:
wide view angle
weak color shift
pressure resistance
MVA:
wide view angle
high contrast ratio
fast response time
Flexible displays
Flexible Displays for wearable technology
Flexible display market
Flexible ChLCD’s
Cholesteric LCD’s
Cholesteric LCD’s with nano pigments for colors
ITO on flexible glass
Dual frequency ChLC display
ChLC display
R2R (Roll-to-Roll technology)
R2R (Roll-to-Roll technology) for ChLCD
Competing technologies: E-ink
Usato per Kindle di Amazon. Difficoltà a creare colori anche al SID Display week
a maggio 2016 è stato annunciato un e-ink paper a 32000 colori.
AMOLED
OLED vs LC for flexible displays
RGB OLED vs IPS LCD
Nanocrystal based quantum dots for LC displays
Emission of nanocrystals for QD
Quantum dots based backlight
Quantum dots LCD
Blu-phase LC
Cubic symmetry in BPLC
simple cubic symmetrical
structures
BPI body centered cubic (bcc)
BPII simple cubic
Molecular alignment in BPLC
Kerr-like electro-optic effect in blu-phase LC
Advantages of Polymer Stabilized BPLC:
Excellent black state through crossed polarizers
Sub-millisecond switching time.
Kerr-like electro-optic effect in blu-phase LC
Blu-phase IPS-LC display
Low voltage Blu-phase IPS-LC display
Quantum dots BP-LCD
LC based tunable laser
Cavity working principle
Synchronous mode
Asynchronous mode
LC based tunable laser tuning range
LC based random lasers
D. Wiersma, Nature Physics vol. 4, p. 359, May 2008
PDLC based random lasers
Applications of random lasers
Lighting
Medical diagnostics
The emission spectrum of cancerous human tissue, when doped with laser dye,
could be distinguished from healthy tissue. This would enable an alternative
strategy for tumour diagnostics.
Biomedical imaging
Different tissue and bone types have different optical structures and
mean free paths. Techniques such as photon-density wave analysis
and diffusing wave spectroscopy, all based on the knowledge of
multiple light scattering in random systems, have already proved
their value in characterizing tissue and monitoring blood flow
during treatment and surgery.
Low cost VCSEL using ChLC
K. Panajotov et al. J. OF LIGHTWAVE TECHNOLOGY, VOL. 32, NO. 1, JANUARY 1, 2014
Phase shifter with SOI/LC slot waveguides
Y. Xing et al. IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 27, NO. 12, JUNE 15, 2015
SOI/LC slot waveguides: simulations
SOI/LC slot waveguides: experimental
Low-k gate OFET based on LC
Kunii et al. IEEE ELECTRON DEVICE LETTERS, VOL. 37, NO. 4, APRIL 2016
Low voltage OFET
Kunii et al. IEEE ELECTRON DEVICE LETTERS, VOL. 37, NO. 4, APRIL 2016
C8-BTBT films with mobility up to 43 cm2 Vs-1 (25 cm2 Vs-1 on average)
Y. Yuan et al. NATURE COMMUNICATIONS, Published 8 Jan 2014, DOI: 10.1038/ncomms4005
Conclusions: always fun working with the LC!
New materials
New physics and new technology
New or alternative device concepts
……………..

lc 32 ga5e

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